What is this hole?

[AgentZero]

So I noticed this hole at the back of my phone. Its an Xperia Z. 
Is it really supposed to be there? or its broken? also dirt can be stuck in there. 

[Thommo]

Can you upload your image to imageshack or box etc and post the link to it please

[AgentZero]

Here

https://imageshack.com/i/ne5m50j

[Amphosys]

ya it has a tiny hole but not like u show in photo.....see this :http://www.gsmarena.com/sony_xperia_z-3d-spin-5204.php

[AgentZero]

Actually it might not be as big as it looks. I just took the picture so close
What does the hole do? My concern is dirt can come inside and it might not be waterproof anymore.

[Thommo · Accepted solution]

The hole is a rear microphone when using video recording and is waterproof

[AgentZero]

Okay thanks. I kinda freaked out when I see some dirt inside it. 

Thanks for the help

[Thommo]

The rear-mounted camera is a massive 13 megapixels and uses the new Exmor RS lens which helps in low lighting conditions.  There is also a single LED flash to help when lighting is not the best but most of the work is down to the RS lens used.  On the back you also have a mic hole at the top for video recording and the XPERIA logo printed in the middle

Source here just above image 9